Control mechanism and stabilizer



July 25, 1950 Filed March 21, 1947 J. M. NISSEN CONTROL MECHANISM AND STABILIZER 2 Sheets-Sheet 1 JAMES m. mssm y 1950 J. M. NISSEN 2,516,142-

CONTROL MECHANISM AND STABILIZER Filed March 21, 1947 2 Sheets-Sheet 2 aga grime/Mom JAMES H. NISSEH Patented July 25,1950

PAT ENT "516,142 CONTROL MECHANISM AND STABIEIZER I 'iamesM. Nissen, Los- Altos,-*Cal-if. VApplicationMarch '21, 1947; Serial No. 736492 4 Claims. (017244-46) tGranted 'under the act of I March 3; 18-83,- :as

The present invention relates to new -'an'd useful' improvements in aircraft, and more particularly'to new and useful improvements iii-"aircraft control mechanism and stability;

In aircraft, conditions of flight stability" may vary with changing load conditions. as the load in an aircraft is changedythe center of gravity may also'be changed to such an extent that stability of the'aircraft may besubstantially affected. While'the invention isgenerally conconcerned' with all flight stability; both stable and unstable, itis particularly concerned withconditions of longitudinal stability and maintenance of constant stick free static'stability'at the control' stick. Many types of variable 10 ads are contemp'late'd' buttheinvention is'illustrated in' connection with a 'fuel tank located in the fuselage and aft of the normal centerot gravity-of the aircraft In certain types-of aircraft, normal longitudinal stick-free stability "occurs when the aft fuel tank isempty, but with a 'fullyserviced tank, the center of gravity is-shiftedrearwardly with resultant conditions of'lbngitudinal intially maintain stick fre'e'stabilityduring variations and shifting of loads lathe aircraft.

Another object of the invention is to control and substantially-maintain stability or an aircraft by automatically applyinga force on the control surface according to shifting of the center of gravity ofthe aircraft in accordance :with variationsin load carriedby the aircraft. 7

'A- further object of the inventiom is to provide means-directly acted=uponby the load for' applying a force onthe control surface to maintain stability of the aircraft Another object of 'the invention is to decrease the stickfree longitudinal stability-"oi anairplane" where the=airplane is too stable due to'thecenter of gravity being too far forward;

A still further obj ect of thevpresentiinvention is the 1 provision of means r'fonautomatically ad- 1 justinglthe stick-:freelongitudinal-stability to a desirablewvalue 'with center ofwgravity shift: on

a an airplanel possessingdower than 2 desirable :sta-

bility;

7 amended April- 30, 1928; 370 O. G. 757) o t2 1 is the provision of meansfor automatically making an unstable airplane stame.

The device illustrated is only one for-in o f-the invention; "The device may consist ofa solid weight and an arm which applies a force onthe elevators. The position of the weighton the arm and-,' hence the load applied on the e1evator, ma-y be a function of the variable load.

The device may be usedto maintain constant 10 longitudinal stability by either increasing-or decreasing thestab-ility'of the airplane with change invariable load.

The invention still further aims to provide a device directly responsive-to the weight of'the load for maintaining"longitudinal stability of the aircraft.

The above and other objects of" the invention will in part be obvious and will be hereinafter more fully pointed out.

In-'theaccompanying drawings:

Fig. '1 is a diagrammatic side elevation of' a grounde'cl' airplane with an aft fuel tank and showingthecontrol mechanism for the elevators;

.Fig. 2' is aschematic view of thecontrol mechanism-and serviced fuel tank in level flight;

Fig-534s a fragmentary horizontal sectional View of the fuel tank;

"Fig. 4 is anenla-rged section taken along-the line -s- 4-or"-Fig. 3; I

Fig.6 is an enlarged detail-side View showing the link and lever connection between the main 'andauxiliarycontrol mechanism; and

Fig. '6' is anend view of Fig. 5. Refe'rrinsmore in detail to the accompanying drawings, and particularly t'oFig'. 1 thereof, the invention vis diagrammatically illustrated as appliedtofaniairplane of a more "or lessconventional type,- such as a low "wing monoplane having" a single seat and' single engine. Asillustrated; the

.air plane consists of afuselage' IEI having 'm'ain Wings- H and a substantially centrally located blister type 'cockpit I 21 The tail 'assembly'ineludes-a fin B; a rudder I4 hingedly connected thereto and including 'atrim tab IS. The stabilizers '16 have elevators l1 hinged theretoand a trim"ta'b 51'. Top andbottom ho'rns18, l9; respectively, on the elevator are conne'cted'by cables S20;2 l,;irespectively, to opposite'arms 22,23" of a control 1ev'er24 mounted on a fixed pivot 25.

'Thecables are suitablytraine'd over idler pulleys 26 A control rod 21 isconnected'tdan'arm 28 depending from the lever 2'4 Iandto the pivoted control stick .2!! for operating the elevators; Similar mechanisinan'la'y'; be providedfor operating Aistillsfurther'object of theapresentinvention .55 hether K 41 3 1 fiilrffifli An auxniary fuel tank so is carried in the fuselage in rear of the cockpit and rearwardly of the center of gravity which is normally located at g for stable level flight. With the particular type of airplane shown, it is stable with the fuel tank empty but with the tank fully serviced, the plane becomes relatively unstable, as the center of gravity is shifted rearwardly. l

Under these conditions the airplane tends either to dive or climb, and will not return to a trim airspeed once the airplane has been displaced from the trim condition. Stability is obtained by use of the device as follows: for a given weight of fuel in the rear gas tank and at a given airspeed the elevator will be at a required angle for straight flight. The weight of the gas on the bellows will put a certain down load on the elevator. This force will be counteracted by a down deflection of the elevator tab so that the airplane is trimmed longitudinally. If the airspeed of the airplane is increased, the down load on the elevator, due to the weight of gasoline on the bellows, remains approximately constant but the up load on the elevator, due to the elevator tab, increases deflecting the elevator up, which noses the airplane up and thereby reduces the speed of the airplane to the trim speed. If the airspeed of the airplane is decreased from the trim airspeed then the down load on the elevator, due to the weight of gasoline on the bellows, becomes greater than the up load on the elevator, due to the elevator tab and the elevator is deflected downward. This noses the airplan down which increases the airspeed of the airplane to the original trim airspeed where the forces again balance.

fuel within the inner casing. Abellows type piston;

, extending annular flange portions 34a, a. The

ends of the wall portion 33 are disposed around the flange portions 34a. 35a and secured thereto by clamping rings 36, 31. Wire rings 38 are arranged in the outward pleated portions of the wall portion 33 for strengthening and reenforcing purposes and are maintained in position by flexible strips 39 of rubber or other suitable flexible material. The bottom header 35 is secured to the bottom of the fuel tank and piston rods 40, 4011 are secured to the top header 34. The piston rods 40, 40a extend through bearings 41, lla, re-

. spectively, mounted in the bottom of the fuel tank which is alsoprovided with vents 42 to the chamber provided within the wall portion 33.

The spaced piston rods serve to guide the bellows inrectilinear movement.-

The free ends of the piston rods are connected by a spacer 43 which is pivotally connected, as at 44, to an arm 45. The arm 45 is pivoted, as at 45a, to the arm 46a of a bell crank lever 46 which is pivotally mounted, as at 41, to a bracket 48. The other arm 46?) of the bell crank is pivotally connected to a link 49 which in turn is pivoted to the end of lever 811 22.- .The opposite lever which is connected to the bottom elevator horn. The lower end of the lever arm 22 is pivotally connected to the cable 20 which in turn is connected to the top elevator horn. The control rod 21 from the control stick is pivotally connected, as at 50, to the arm 28 for effecting movement of the lever 24 about the pivot. 25. Thus, a rear- .Ward pull on'the control stick will effect clockwise movement of the lever 24 and a pull on the cable 20 connected to the top horn I8, so that the elevators will be moved upwardly. Similarly, a

'forward push on the control stick will effect counterclockwise movement of the lever 24 and a pull on the cable 21 connected to the bottom horn l9, sothat the-elevators will be moved downwardly.

In the particular installation, normal stick-free stabilityoccurs when the auxiliary fuel tank 30 is empty. The wall portion 33 of the piston is constructed so as to oifer little or no resistance tomovement of the elevator controls, and during vflight,thepressures on. the elevators will tend to maintain them inftheir'required position with the piston wall33extended somewhat upwardly in the inner; casing. Thus, when the tank is empty, substantially no 'disruptihg forces are exerted on the elevatorcontrols'so that the airplane remains longitudinally. stable. However, when the tank 30 is serviced and full of fuel, the weight of the column of fuel within the inner casing tends to force, the piston downwardly to collapse the wall portion 33. And too, the fully serviced tank tends to shift the center of gravity rearwardlyto the pointgf. and thiscauses the airplane to nose up when a given setting of the elevator trim tab or adjustable stabilizer is maintained during flight. However, the downward movement of the I piston rods 48, 49a operates through the arm 45 torotate the. bell crank 46 in a clockwise direction and the lever 24 in a counter-clockwise direction so as .to exert a pull on the cable. 20 which will shift the elevators slightly downwardly to counteract the;tendency of the airpl ane to nose up.

As the fuel. is used and the level thereof reduced,

the weight .on the-piston is lessened so that the of the piston is formed so as to offer substantially no resistance to its being extended when the tank is empty and the airplane isin normal longitudinal stability; .With such an arrangement, substantially no resistance is offered to the downward movement of; the piston under the influence of the weight of the fuel in the inner casing.

From the foregoing description, it will be seen that an extremely simple, yet efficient mechanism is provided for maintaining the elevators or other control surfaces: at positions such that stability of an aircraft, iparticularly longitudinal stability thereof, in flight, will be maintained regardless :of the shiftingpositions of the center of gravity as a load,.such as an auxiliary fuel tank, carried by the aircraft varies during flight. The weight of the lo'acl'actswon the piston or other weight responsive-devicesuitable'for the piupose. Thus,

the control stick is shifted to positions. correarm 23 is pivotally"conne'cted to the cable 2I=" 5-"sponding**t0' positions of the elzava'to'rs but is maintained in stick-free static stability in all such positions by the influence of the piston controlled mechanism on the main control system. or course, such influence is assisted by the action of the airstream on the elevators and the elevator trim tab or adjustable stabilizer or other control surfaces and the pressure within the fuel tank.

While one form of the invention has been shown for purposes of illustration, it is to be clearly understood that various changes in the details of construction, arrangement of parts and operation thereof may be changed without departing from the spirit and scope of the invention contemplated and as set forth in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What I claim is:

1. In aircraft having a tendency toward longitudinal instability in flight caused by a shifting of the center of gravity thereof as a result of variations in the weight of a load carried thereby at a point removed from the normal center of gravity, the combination of elevator control surfaces, operating mechanism for said control surfaces, a fuel tank located aft of the center of gravity of the aircraft, a piston located in said tank and constructed and arranged to be moved in response to fuel level in said tank, and connections between said piston and said operating mechanism for shifting said operating mechanism and said control surfaces according to the variations of fuel level in said tank whereby to maintain normal longitudinal stability in flight regardless of shifting of the center of gravity of the aircraft.

2. In aircraft having a fuel tank located aft of the normal center of gravity of the aircraft which fuel tank when filled shifts the center of gravity rearwardly to cause longitudinal instability in flight, the combination of elevator control surfaces, operating mechanism for said control surfaces, a device located in saidfuel tank and movable in response to variation in the fuel level therein, and linkage means connecting said device to said operating mechanism for shifting said control surfaces through said operating mechanism to positions compensating for the changing positions of the center of gravity whereby to maintain longitudinal stability of the aircraft in flight.

3. In aircraft having a fuel tank located aft of the normal center of gravity of the aircraft which fuel tank when filled shifts the center of gravity rearwardly to cause longitudinal instability in flight, the combination of elevator control surfaces, an inner tubular casing within said fuel tank and apertured to permit the fuel level of the tank to be present therein, piston means movable axially in said casing in response to the fuel level in said tank, a piston rod connected to said piston means and extending exteriorly of said tank, a link connected to said piston rod, and bell crank lever means connected to said link and to said control surfaces for effecting movement of said control surfaces in response to variation in the fuel level in said tank whereby to compensate for changing positions of the center of gravity of the aircraft.

4. In aircraft having a fuel tank located aft of the normal center of gravity of the aircraft which fuel tank when filled shifts the center of gravity rearwardly to cause longitudinal instability in flight, the combination of elevator control surfaces, an inner tubular casing within said fuel tank and apertured to permit the fuel level of the tank to be present therein, a bellows piston having the interior thereof open to pressure in the aircraft and movable axially in said casing in response to the fuel level in said tank, a piston rod connected to said bellows piston and extending exteriorly of said tank, a link connected to said piston rod, and bell crank lever means connected to said link and to said control surfaces for effecting movement of said control surfaces in response to variation in the fuel level in said tank whereby to compensate for changing positions of the center of gravity of the aircraft.

JAMES M. NISSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

